This study investigated the spatiotemporal variation of fish larvae assemblages and their relationships with environmental factors in the coastal waters of Saryang and Yokji Islands, Korea, from June 2024 to April 2025. During the study period, surface water temperature ranged from 6.1 to 30.3°C and salinity ranged from 28.25 to 33.96 psu, showing clear seasonal variability. A total of 23 fish larvae taxa belonging to 5 orders and 14 families were identified. Dominant taxa included Parablennius yatabei, Engraulis japonicus, Sebastiscus marmoratus, and Hexagrammos agrammus. Larval abundance ranged from 15 to 1,137 ind. 1,000 m-3, with the highest density and species diversity observed in early summer. Cluster analysis revealed three seasonal assemblages: summer-autumn, winter, and winter-spring groups. Redundancy analysis (RDA) indicated that temperature, salinity, and several copepod taxa were associated with fish larvae distribution, while the cumulative variance explained by the first two axes was 23.9%. These results suggest that fish larvae assemblages in the Saryang and Yokji Islands coastal area are partly related to seasonal environmental gradients and zooplankton composition, but are also influenced by multiple factors including hydrodynamic transport and coastal physical structures. This study provides baseline ecological information on seasonal fish larvae assemblages in a multiisland coastal system and highlights the ecological importance of this area as a spawning and nursery ground for coastal fish populations.

This study examined the spatiotemporal distribution and community structure of fish larvae in the coastal waters of Geoje Island, Korea, from June 2024 to April 2025, and assessed the impact of environmental factors on larvae assemblages. The abundance of fish larvae varied significantly, ranging from 63 to 12,330 individuals per 1,000 m3. A total of 20 taxa from 14 families and 6 orders were identified. Dominant taxa included Clupea pallasii, Parablennius yatabei, Hexagrammos agrammus, Engraulis japonicus, Sebastiscus marmoratus, Sebastes schlegelii, Repomucenus valenciennei, and Rudarius ercodes. Cluster and nMDS analyses identified three distinct seasonal assemblages: a summer-autumn assemblage, a transitional assemblage, and a winter-spring assemblage. The summer-autumn assemblage was dominated by coastal and pelagic species, including Engraulis japonicus and Parablennius yatabei, while the winter-spring assemblage was characterized by coldseason spawning species such as Clupea pallasii and Hexagrammos agrammus. Redundancy analysis (RDA) revealed that temperature and salinity were the primary environmental drivers of fish larvae assemblages (p<0.01). Temperature was strongly correlated with Axis-1, which represents the main environmental gradient influencing larvae assemblages. Additionally, the copepod Acartia omorii showed a strong association with Axis-2, indicating that zooplankton community composition played a secondary role in shaping larvae assemblages. Environmental variables accounted for 26.3% of the total variance, suggesting that larvae distributions were affected by environmental conditions, hydrodynamic transport, spawning strategies, and biological interactions. These findings provide essential baseline information for fisheries resource management and coastal ecosystem monitoring.